Ken Burns’ PBS series, The National Parks: America’s Best Idea, showcases the history and importance of preserving America’s most beautiful, unique, and pristine natural wonders. Among these inspiring entities is Mount Rainier, a volcanic peak 14,410 feet high located in the snowcapped Cascades cutting through western Washington. In 1899 Mount Rainier National Park became the fifth national park to be established in the United States, and since the late 1960s, when statistical tracking began, it has received anywhere between 1.5 million and 2.2 million visitors annually.

While Rainier’s impressive size and dynamic landscapes are awe-inspiring, it is the mountain’s potential to unleash a storm of ash and lava that is simultaneously fascinating and unsettling. Rainier is a dormant volcano, and because of its nearness to the Seattle-Tacoma-Bellevue metropolitan area, which has a population of more than 3.3 million people, it is the focus of intense monitoring activities and research aimed at predicting eruptions.

Rainier is a stratovolcano, and thus it was formed from repeated lava eruptions and pyroclastic flows, which produced alternating layers of lava and ash. It is considered a young volcano—a mere one million years old—when compared to the peaks around it, which have been around for more than 12 million years. Most of those old peaks are classified as extinct volcanoes, making Rainier, as well as its southern neighbor, Mount Saint Helens, which is an active volcano, especially interesting in terms of geologic history.

Rainier also is the most glaciated mountain in the contiguous United States; it has 25 distinct glaciers covering about 35 square miles. Today, however, the mountain’s jagged glaciers are remnants of their former selves. Those on the south-facing slopes have retreated significantly in the last century, much more so than the glaciers on the northern slopes. Beginning in the 1980s, the balance between glacial accumulation and ablation tipped toward the latter, when summer temperatures suddenly increased in the Pacific Northwest, obtaining annual averages higher than in previous decades. This was compounded by the onset of dry winters, which meant less snow and ice accumulation and therefore less glacier building activity.

Rainier’s glaciers overlie layers of volcanic rock fragments and other debris, and as temperatures have warmed locally, melting glacier ice has become a serious concern, since it can cause destructive lahars, or volcanic mudslides. Scientists have identified the remains of numerous such flows that occurred on Rainier in the last several thousand years, and these, in addition to glaciers and landslides, have sculpted the mountain, carving out valleys and generating large deposits of debris. Other factors such as small earthquakes also have shaped Rainier by giving rise to landslides and avalanches, and more than 20 minor earthquakes occur at Rainier each year, a figure exceeded in the lower 48 only by Mount Saint Helens.

Rainier last erupted in the 1840s, and all the factors described above—its proximity to a large metropolitan area, the increased chance of lahars due to warming local temperatures, and its level of seismic activity—has led to its inclusion as a Decade Volcano. Decade Volcanoes, of which there are 16, were chosen by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) for scientific investigation into the forces and processes that form Earth’s features. The project will also attempt to identify and develop methods for accurately predicting eruptions in order to provide time for sufficient warning and evacuation, thereby protecting peoples’ lives and mitigating some effects of a disaster.

Though the destruction to human life and property would be staggering if Rainier erupted, there also would occur substantial losses in the unique collection of plants and animals that inhabit the mountain’s slopes and surrounding lands. Old growth forests blanket the landscape at lower elevations and make up about 58 percent of the park’s area. These forests are home to giant trees, such as Western red cedar and Douglas fir, some stands of which are believed to be more than 1,000 years old. The higher subalpine region, between elevations of 5,000 and 7,000 feet, is characterized by subalpine fir and Englemann spruce, shrubs such as serviceberry, and grasses such as green fescue. The alpine region, the highest ecosystem and occupying about 19 percent of the park, is split between low vegetation, mostly grasses, and snow and ice. Animals such as pikas and mountain goats are found almost exclusively in the alpine region, while marmots, a type of giant ground squirrel, traverse both the subalpine and the alpine elevations.

Although few of Rainier’s visitors venture to its upper limits, the significance of the mountain—that it is home to rapidly receding alpine glaciers and that it could erupt in this century—captures our imaginations in ways indescribable. The park itself is accommodating to the most adventurous individual as well as to the curious passerby. There are plenty of trails to explore and geological phenomena to discover. There also is a diverse lot of flora and fauna to see—Rainier is home to more than 800 species of plants, nearly 160 species of birds, and a variety of amphibians, fish, mammals, and insects. In some ways, however, to really experience Rainier, to really feel its power and magnificence, one must ascend its slopes, climb up to where the air is thin, the whipping winds are ever-present, and the snowfields are blinding. The experience is unforgettable.